1. Field of the Invention
The present invention relates to a hydrolyzable and biodegradable resin composition in consideration of the global environment and more particularly relates to a decomposable resin composition that has a low impact on the environmental and a method of treating the resin composition for lowering the environmental impact.
2. Related Background Art
In the past, humans successively produced useful domestic and industrial materials by employing coal chemical technologies and then petrochemical technologies. In particular, polymer materials may be symbolic examples. There have been produced useful resins including plastic materials such as polyethylene, polypropylene and polyvinyl chloride and rubbers such as polyisoprene and polybutadiene. Further, recently, resin materials having particularly excellent characteristics have been developed, including polyimide resins, which have heat and impact resistance, and full-aromatic liquid crystal polymers.
However, these resins are not biodegradable and remain unchanged in the environment for long after being discarded, imposing a significant, negative burden on the global environment. The waste from industries and domestic life has become a serious social problem. Today, there is an increased expectation for materials and products to be environmentally friendly. At the same time, it is preferable that these products and materials be manufactured with a minimal possible reliance on natural resources.
For such a purpose, biodegradable polymers that are easily decomposed in the environment have been developed. A substantial object is to obtain a resin that satisfies contradicting properties such as stability during use and quick decomposition when discarded. Further, based on the purpose, the decomposition speed itself is required to be controlled.
Consequently, the purpose of the present invention is to provide a decomposable resin composition, which is stable at the time of use, quickly decomposed when discarded and whose decomposition speed can be controlled.
The inventor of the present invention conducted an extensive investigation in order to solve the problem and found that the above purpose can be achieved by mixing a compound capable of generating an acid or a base by light irradiation or heating at a desired time with a decomposable resin and then generating an acid or a base in the decomposable resin by carrying out light irradiation and/or heat treatment at the desired time so as to promote the decomposition of the resin and thus achieved the invention.
The present invention includes a resin composition comprising, in a hydrolyzable and biodegradable resin, an agent generating an acid upon exposure to light and/or an agent generating a base upon exposure to light.
Further, the present invention provides a resin composition comprising, in a hydrolyzable and biodegradable resin, an agent generating an acid upon exposure to heat and/or an agent generating a base upon exposure to heat.
Further, the present invention provides a resin composition comprising, in a hydrolyzable and biodegradable resin, an agent generating an acid upon exposure to light and/or an agent generating a base upon exposure to light together with an agent generating an acid upon exposure to heating and/or an agent generating a base by heating.
Further, the present invention provides a method of producing a resin composition comprising the steps of: providing a resin composition comprising, in a hydrolyzable and biodegradable resin, an agent generating an acid upon exposure to light and/or an agent generating a base upon exposure to light; subjecting the resin composition to light irradiation and/or heat treatment to decompose the resin composition to monomers; polymerizing the monomers to produce a decomposable resin; and mixing compounds generating an acid or a base by light irradiation or heating with the decomposable resin.
Further, the present invention provides a method of treating a resin composition comprising the steps of: providing the resin composition comprising, in a hydrolyzable and biodegradable resin, an agent generating an acid upon exposure to light and/or an agent generating a base upon exposure to light; and subjecting the resin composition to light irradiation.
Further, the present invention provides a method of treating a resin composition comprising the steps of: providing the resin composition comprising, in a hydrolyzable and biodegradable resin, an agent generating an acid upon exposure to light and/or an agent generating a base upon exposure to light; subjecting the resin composition to light irradiation; and thereafter carrying out a heat treatment.
Further, the present invention provides a method of treating a resin composition comprising the steps of: providing the resin composition comprising, in a hydrolyzable and biodegradable resin, an agent generating an acid upon exposure to heat and/or an agent generating a base upon exposure to heat; and subjecting the resin composition to a heat treatment.
Further, the present invention provides a method of treating a resin composition comprising the steps of: providing the resin composition comprising, in a hydrolyzable and biodegradable resin, an agent generating an acid upon exposure to light and/or an agent generating a base upon exposure to light together with an agent generating an acid upon exposure to heat and/or an agent generating a base upon exposure to heat; and subjecting the resin composition to light irradiation and a heat treatment.
As the decomposable resin to be employed in the present invention, usable are a wide range of well-known biodegradable, hydrolyzable polyesters. Especially preferable are polylactic acid, polylactic acid-aliphatic polyester copolymers and copolymers of saccharides and dicarboxylic acids having a structure defined as the following formula: 
(Where (Sacch) denotes the saccharide structure and R denotes an alkylene group or a divalent aromatic ring.).
Monosaccharides are usable for the saccharide structure portion in the formula, including neutral saccharides such as D-glycelaldehyde, D-dihydroxyacetone, D-xylose, D-glucose, D-fructose, D-mannose, D-galactose and L-fucose; acidic saccharides such as D-glucuronic acid and L-iduronic acid; aminosaccharides such as D-glucosamine, D-galactosamine, N-acetylglucosamine, N-acetylgalactosamine and N-acetylmuramic acid; dialuric acid such as N-acetylneuraminic acid; glycitols such as glycerol and inositol; and disaccharides such as saccharose, maltose, lactose, cellobiose and trehalose. Further polysaccharides are usable such as amylose, cellulose, chitin, chitosan, hyaluronic acid, chondoroitin hexasulfuric acid, keratosulfuric acid and heparine.
On the other hand, R in the formula may preferably be an alkylene of 1 to 12 carbons or a divalent aromatic group, for example, phenylene or naphthylene. Examples of a dicarboxylic acid containing such groups are aliphatic dicarboxylic acids, such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid and 1,10-didecanedicarboxylic acid; and an aromatic dicarboxylic acid, such as terephthalic acid, isophthalic acid, orthophthalic acid and naphthalenedicarboxylic acid.
Among the polymers defined by the formula, especially preferable are polyesters represented by the following formula (II), such as polyesters produced from D-glucose and aliphatic dicarboxylic acids having 5 to 10 carbons and polyesters produced from compounds derived from D-glucose by substituting a hydroxyl group with an alkyl group, a hydroxyalkyl group and the like and aliphatic dicarboxylic acids having 5 to 10 carbons: 
(Where R denotes an alkylene; R1, R2 and R3 separately denote hydrogen atom, an alkyl of 1to 10 carbons, or a hydroxyalkyl.).
Especially, in the case of using D-glucose in the portion of the saccharide structure, D-glucose can be obtained by decomposition of cellulose. From a viewpoint of recycling of immensely consumed paper, that is remarkably significant. The decomposition of cellulose can be carried out by chemical decomposition, such as hydrolysis with an acid or a base or by biodegradation using microorganism, such as employing cellulase.
By combining a proper acid- or base-generating agent generating an acid or a base upon irradiation with an electromagnetic wave or charged particles with these decomposable resins, decomposition can be promoted. This decomposition cannot be achieved at a desired time solely by biodegradation. Conventionally, as an example of a material containing a polymer having acid-decomposable functional groups and an acid-generating agent, for example, Japanese Patent Application Laid-Open No. 9-179302 discloses a photoresist to be used for an electronic device fabrication. Further, Japanese Patent Application Laid-Open No. 10-171120 discloses the usage of a natural material as one component for such a resist material composition. However, the natural materials are not all biodegradable and the compositions that are biodegradable do not contain an acid-generating agent or a base-generating agent.
As the photolytically acid-generating agent (the agent generating an acid by light) to be preferably used in the present invention, available are well-known compounds such as sulfonium salts, which can be, for example, a triphenylsulfonium trifluoroemethylsulfonic acid salt represented by the formula (III), and iodonium salts, which can be, for example, diphenyliodonium hexafluoroantimonate represented by the formula (IV). These photolytically acid-generating agents may be used solely or in combination with a plurality of the acid-generating agents. An amount of a photolytically acid-generating agent may preferably be 0.1 to 20% by weight and especially preferably 1to 5% by weight in a decomposable resin. 
As a photolytically base-generating agent (the agent generating a base by light), well-known compounds are usable, such as compounds represented by the formula (V) or the formula (VI). These compounds are disclosed in, for example, H. Tachi, M. Tunooka, J. Photopolymer Science and Technology, 12(2), 313(1999); T. Nishikubo, A. Kameyama, Y. Toya, Polymer J. 29(5), 450(1997). 
Photolytically base-generating agents to be added may be used solely or in combination with a plurality of base-generating agents. An amount of a photolytically base-generating agent may preferably be 0.1 to 20% by weight and especially preferably 1to 5% by weight in a decomposable resin.
In the case where a decomposable resin composition of the present invention is required to be stable during use, a photolytically acid-generating agent or a photolytically base-generating agent to be used is required not to absorb visible light, but to absorb light, electromagnetic waves, or a charged particle beam irradiated thereto at the time when the decomposition treatment or discarding is carried out.
In the case where a decomposable resin composition containing such a photolytically acid-generating agent or a photolytically base-generating agent is to be subjected to the decomposition treatment or to be discarded, the resin composition is irradiated with electromagnetic waves or a charged particle beam. A light source to carry out the irradiation or an irradiation source may properly be selected corresponding to the absorption characteristics of the resin composition for the electromagnetic waves or a charged particle beam. For example, in the case of a decomposable resin composition with a relatively high light transmissivity, light with slightly shorter wavelengths than that of visible light are suitable. More practically, light in a range of 200 nm to 380 nm is employed. Further, if a decomposable resin composition, such as a colored resin, is extremely inferior in light transmissivity, electromagnetic waves such as X-rays and xcex3-rays with even shorter wavelengths may be employed. Further, an electron beam and an ion beam with a high accelerating voltage may be used. The irradiation dose of light and electromagnetic waves may preferably be 1 to 10,000 mJ/cm2 or the irradiation dose of a charged particle beam may preferably be 1 to 1,000 xcexcC/cm2.
In the present invention, in the case where a compound generating an acid or a base upon exposure to heat is combined with a decomposable resin, for example, hydrochloric acid salts are usable. Also, as a compound generating a base upon exposure to heat, for example, silazane compounds are usable, such as octamethylcyclotetrasilazane, and ammonium salts, such as a carboxymethylcellulose ammonium salt. An amount of such a compound may preferably be 0.1 to 20% by weight and especially preferably 1 to 5% by weight in a decomposable resin. The heating temperature may preferably be 50 to 150xc2x0 C. and the heating duration may preferably be 30 to 120 minutes.
In the treatment of a decomposable resin composition of the present invention, the decomposition speed of the resin can be controlled corresponding to the amount of an acid or a base to be generated by light irradiation or heating. The amount of an acid or a base that is generated can be controlled by controlling an amount of the acid-generating agent or the base-generating agent, the irradiation dose of the electromagnetic wave or the charge particle beam, or the heating conditions. Further, an acid-generating agent and a base-generating agent are made to coexist to control the concentration of the practically effective acid generated to subsequently control the decomposition speed.
Prior to being discarded, a used decomposable resin composition or an article molded from the composition in the present invention, light irradiation or a heat treatment is carried out to decompose it within a short time period in the environment.
A decomposable resin decomposed into monomers by a method according to the present invention may be recycled by synthesizing a decomposable resin again by recovering the monomers. That is, using a polymer produced from, for example, D-glucose and adipic acid, D-glucose and adipic acid obtained by the decomposition of an acid or a base generated from the acid-generating agent or the base-generating agent are again polymerized to synthesize the decomposable polymer. A decomposable resin composition is obtained by mixing an acid-generating agent and a base-generating agent by light irradiation or heating with such as resin. The obtained resin composition is used again in a general manner and made semi-permanently usable in a recycling system where the decomposition and recovery are carried out.